The short answer
Record accumulated kWh at the start and end of complete cycles or representative complete days, then subtract the readings. Retain the model, programme, load, settings and conditions. A sample reports observed energy; applying it to an annual routine is a separately stated projection, not an annual measurement.
Record accumulated kWh, not just live watts
A watt reading shows power at that moment. An accumulated kWh reading shows energy used across a period. For a cycling appliance, a single active-power snapshot cannot establish the cost of a day or year.
Use an appropriate energy monitor or existing appliance-only metering information. Follow its ratings and instructions; this method does not require opening equipment, changing wiring or bypassing controls. A whole-home meter includes other loads and cannot assign its entire change to one appliance.
Keep a short measurement record
- Identify the appliance and the energy boundary: one appliance, one complete task or a combined group.
- Record the starting kWh reading and time. Reset a monitor only as its instructions allow.
- Run the ordinary routine. Include a complete programme for a cycle measurement or complete days for a daily average.
- Record the ending reading and time. Subtract the starting reading if the counter was not reset.
- Note the programme, load, settings and room conditions that might explain variation.
For an illustrative example, a monitor starts at 12.4 kWh and ends at 20.1 kWh after seven complete days. Energy in the sample is 20.1 − 12.4 = 7.7 kWh. Enter the difference, not the ending counter value.
A measurement record you can print or copy
Use the measurement journal to retain the starting and ending counters, dates, comparable cycle or complete-day count, model, monitor and conditions. It calculates the measured difference and keeps optional price and annual routine assumptions separate. Save up to 100 observations in your browser, download them as CSV, print the current record or transfer compatible inputs into a calculator. Export records you want to retain before clearing browser data.
Use your browser’s print command to retain this guide and blank record. Fill in actual observations before calculating. This table contains no reported measurements.
| Field to record | Your observation |
|---|---|
| Observer and local time zone | ____________________ |
| Exact appliance model and configuration | ____________________ |
| Monitor model, rating and energy resolution | ____________________ |
| Energy boundary: one device, task or named group | ____________________ |
| Start date/time and starting counter in kWh | ____________________ |
| End date/time and ending counter in kWh | ____________________ |
| Complete days or completed cycle count | ____________________ |
| Programme, temperature and dryness/settings | ____________________ |
| Load amount and relevant room conditions | ____________________ |
| Interruptions, unusual use or counter reset | ____________________ |
| Ending minus starting kWh | ____________________ |
| Currency, consumption-related price and tariff date | ____________________ |
Retain a photo or original reading when useful. Leave out account numbers and private household details if you share the record. For washing or drying, repeat the same defined task before describing an average; keep a different programme in a separate group.
Distinguish an observation from an annual projection
An observation reports the energy and conditions actually recorded. A projection applies those readings to an explicitly chosen routine, use period and price. Keep both visible: sample kWh, sample duration or task count, annualization assumption, then modeled cost.
One family’s fridge week would not establish typical US or European fridge consumption. A single load would not prove that every load or season uses the same energy. Repeating measurements under relevant conditions can show the variation observed; it does not turn the sample into a standardized label test.
Watt & Home identifies sourced declarations, attributed research measurements and clearly marked scenario assumptions. Our US dryer case study analyzes published household measurements collected by external researchers. We do not present invented readings as firsthand tests. The documented appliance examples retain their manufacturer or registry basis separately from this measurement method.
Match the sample to the calculator
| What the sample covers | Suitable input |
|---|---|
| One complete washer or dishwasher programme | Its measured kWh as a per-cycle figure |
| Several comparable completed cycles | Total kWh divided by the number of cycles |
| Complete appliance-use days | Total kWh and measurement days in measured mode |
| A continuously used fridge’s representative days | A stated daily projection or carefully annualized figure |
| A few active minutes or a partial programme | Does not establish a complete-day or complete-cycle average |
The electricity calculator projects a complete-day average across your chosen use days. It does not turn a ten-minute measurement into a daily profile. For a meal, the cooking comparison accepts measured whole-meal kWh, including the preheating and batches already captured.
The journal sends a daily sample’s total kWh and complete-day count to measured mode. For washer, dryer and dishwasher cycles, it sends the sample average as kWh per cycle. A household-plan transfer starts a new plan with one row. Missing price and routine values stay empty for your own entry; review the destination before calculating. The guided start can help if you are unsure which input method fits.
Annualize a fridge sample carefully
Using the illustrative 7.7 kWh across seven complete days and £0.28/kWh:
| Calculation | Result |
|---|---|
| 7.7 ÷ 7 | 1.1 kWh per sampled day |
| 1.1 × 365 | 401.5 kWh per modeled year |
| 401.5 × £0.28 | £112.42 per modeled year |
This holds the sampled average constant. It is not a standardized label test or proof that the week represents all seasons. Different room conditions, loading and defrost activity can affect the sample. Repeat the observation under relevant conditions and retain the original readings.
For a seasonal appliance, use the intended use days rather than automatically selecting 365. Another illustrative sample of 4.8 kWh across three days, repeated across 20 comparable use days, gives 32 kWh and £8.96 at £0.28/kWh.
Average cycles using completed tasks
If three comparable completed cycles use an illustrative 1.65 kWh, the sample average is 0.55 kWh/cycle. At four such cycles each week, 0.55 × 4 × 52 = 114.4 kWh/year, costing £32.03 at the illustrative rate.
Do not average unrelated programmes together and then describe the result as the energy of a specific programme. Use distinct task groups in the household planner when their frequency differs.
Compare compatible boundaries
A socket measurement may exclude an external hot-water supply. A published label figure can use different conditions or include related energy. Check both before treating a difference as an inaccurate label.
Measured energy already includes cycling and idle use inside the sample. Do not apply another assumed duty-cycle reduction or add those same components again. Keep your measurement notes and tariff date with the saved or printed result.